1. Field of the Invention
The present invention relates to methods and apparatus for the treatment of presbyopia and the treatment and prevention of glaucoma using dual-beam scanning lasers.
2. Prior Art
Corneal reshaping, including a procedure called photorefractive keratectomy (PRK) and a new procedure called laser assisted in situ keratomileusis, or laser intrastroma keratomileusis (LASIK), has been performed by lasers in the ultraviolet (UV) wavelength of 193-213 nm. Commercial UV refractive lasers include ArF excimer lasers at 193 nm and other non-excimer, solid-state lasers, such as the one patented by the present inventor in 1992 (U.S. Pat. No. 5,144,630). Precise, stable corneal reshaping requires lasers with strong tissue absorption (or minimum penetration depth) such that the thermal damage zone is at a minimum (less than few microns). Furthermore, accuracy of the procedure of vision correction depends on the amount of tissue removed in each laser pulse, in the order of about 0.2 microns. Therefore, lasers at UV wavelengths between 193 and 213 nm and at the mid-infrared wavelengths between 2.8 and 3.2 microns are two attractive wavelength ranges which match the absorption peak of protein and water, respectively.
The above-described prior arts are however limited to the use of reshaping the corneal surface curvature for the correction of myopia and hyperopia. A variation of farsightedness that the existing laser surgery procedures will not treat is presbyopia, the gradual age related condition of suddenly fuzzy print and the necessity of reading glasses. When a person reaches a certain age (around 40), the eyes start to lose their capability to focus sharply for near vision. Presbyopia is not due to the cornea but comes about as the lens loses its ability to accommodate or focus sharply for near vision as a result of loss of elasticity that is inevitable as people age.
Thermal lasers such as Ho:YAG have been proposed for the correction of hyperopia by laser-induced coagulation of the corneal. The present inventor has also proposed the use of a laser-generated bifocal for the treatment of presbyopic patients but fundamental issues caused by age of presbyopic patients still remains unsolved in those prior approaches.
To treat presbyopic patients, or the reversal of presbyopia, using the concept of expanding the sclera by mechanical devices has been proposed by Schaker in U.S. Pat. Nos. 5,529,076, 5,722,952, 5,465,737 and 5,354,331. These mechanical approaches have the drawbacks of complexity and are time consuming, costly and have potential side effects. To treat presbyopia, the Schaker U.S. Pat. Nos. 5,529,076 and 5,722,952 propose the use of heat or radiation on the corneal epithelium to arrest the growth of the crystalline lens and also propose the use of lasers to ablate portions of the thickness of the sclera. However, these prior arts do not present any details or practical methods or laser parameters for the presbyopic corrections. No clinical studies have been practiced to show the effectiveness of the proposed concepts. The concepts proposed in the Schaker patents regarding lasers suitable for expanding the sclera tissues were incorrect in that the proposed lasers did not identify those which are "cold lasers" and can only conduct the tissue ablation rather than thermal burning of the cornea. Furthermore, the clinical issues, such as accuracy of the sclera tissue removal and potential tissue bleeding during the procedures, were not indicated in these prior patents. In addition, it is essential to use a scanning laser to achieve the desired ablation pattern and to control the ablation depth on the sclera tissue.
One objective of the present invention is to provide an apparatus and method to obviate these drawbacks in the above Schaker patents.
It is yet another objective of the present invention to provide an apparatus and method which provide the well-defined laser parameters for efficient and accurate sclera expansion for presbyopia reversal and the treatment and preventing of open angle glaucoma.
It is yet another objective of the present invention to use a scanning device such that the degree of ciliary muscle accommodation can be controlled by the location, size and shapes of the removed sclera tissue.
It is yet another objective of the present invention to define the non-thermal lasers for efficient tissue ablation and thermal lasers for tissue coagulation. This system is able to perform both in an ablation mode and in a coagulation mode for optimum clinical outcomes. It is yet another objective of the present invention to provide an integrated system in which dual-beam lasers can be scanned over the corneal surface for accurate ablation of the sclera tissue without bleeding, with ablation and coagulation laser beams simultaneously applied on the cornea.
It is yet another objective of the present invention to define the optimal laser parameters and the ablation patterns for best clinical outcome for presbyopia patients, where sclera expansion will increase the accommodation of the ciliary muscle.
It is yet another objective of the present invention to provide the appropriate scanning patterns which will cause effective sclera expansion.